What is vision loss?

Vision is our most precious special sense. Nearly half of the human brain is engaged in vision-related activities. Vision loss is any reduction in the ability to see, including blurred vision, cloudy vision, double vision, blind spots, poor night vision, and loss of peripheral vision (tunnel vision). Vision loss may affect one or both eyes, it may occur gradually or suddenly, and it may be partial or complete. Vision changes may originate in the eyes themselves or may be caused by many different conditions that affect the brain or even the whole body.

The path of light rays, which form all the images we perceive, begins at the cornea, the clear “window” in the front of the eye. The iris, which is the colored part of the eye, controls the pupil size and allows light rays to enter the eye and pass through the lens. This helps to focus the rays onto the retina, which is the light-sensitive layer on the inner surface of the eye. Damage caused by trauma, infection, inflammation, or other changes in these structures can reduce vision. The shape of the eye is maintained by the pressure of the fluid inside the eye against the sclera, the white part of the eye, and the cornea. Conditions that affect the clarity or pressure of the fluid in the eye can also affect vision.

The optic nerve organizes the visual impulses from the retina and transmits them to the brain for interpretation. Damage to the nerve due to inflammation, autoimmune disease, or decreased blood supply can lead to vision loss, as can conditions that affect the brain either generally or in the specific locations of the brain that interpret vision.

Some common causes of vision loss include eye trauma, clouding of the lens (cataract), increased eye pressure (glaucoma), retinal damage due to diabetes (diabetic retinopathy), breakdown of the central portion of the retina (age-related macular degeneration), retinal detachment, inflammation of the optic nerve (optic neuritis), and stroke. Some medications can also affect vision.

Vision loss can be permanent and may be a symptom of a serious medical condition. Seek prompt medical care for any type of vision loss. Seek immediate medical care for sudden vision changes, trauma, eye pain or redness, double vision, partial or complete blindness, or vision loss that occurs like a shade dropping or a curtain closing. Immediate medical care is also necessary if vision loss is accompanied by a severe headache, sudden weakness or numbness on one side of the body, altered level of consciousness, dizziness, difficulty speaking or understanding speech, or loss of sensation. Even temporary vision loss should be treated as an emergency.

What other symptoms might occur with vision loss?

Vision loss may accompany other symptoms, which will vary depending on the underlying disease, disorder or condition. Conditions that affect vision can also involve other body systems.

Eye symptoms that may occur along with vision loss

Vision loss may accompany other symptoms affecting the eye including:

• Crooked eye (strabismus)
• Dilated pupilsor pupils that do not respond to light
• Discharge from the eye
• Droopy eyelid
• Eye pain
• Increased sensitivity to light
• Itchy eye
• Red, sore eyes(bloodshot eyes)
• White pupil

Other symptoms that may occur along with vision loss

Vision loss may accompany symptoms related to other body systems. These symptoms include:

• Abnormal gait
• Difficulty speaking
• Fatigue
• Feeling very thirsty
• Frequent urination
• Headache
• Impaired balance and coordination
• Muscle spasms
• Nauseawith or without vomiting
• Numbness or tingling
• Tremor
• Unexplained weight loss
• Weakness (loss of strength)

Serious symptoms that might indicate a life-threatening condition

In some cases, vision loss may be a symptom of a life-threatening condition that should be immediately evaluated in an emergency setting. Seek immediate medical care (call 911) if you, or someone you are with, have any of these life-threatening symptoms including:

• Abnormal pupil size or nonreactivity to light
• Change in level of consciousness or alertness, such as passing out or unresponsiveness
• Change in mental status or sudden behavior change, such as confusion, delirium, lethargy, hallucinationsand delusions
• Garbled or slurred speechor inability to speak
• High fever(higher than 101 degrees Fahrenheit)
• Loss of bladder or bowel control
• Numbness or weaknesson one side of the body
• Seizure
• Severe headache or eye pain
• Trauma, such as bone deformity, burns, eye injuries, and other injuries

What causes vision loss?

A wide variety of diseases, disorders and conditions can cause vision loss. Vision loss may originate in the eyes themselves or may be caused by many different conditions that affect the whole body. Trauma, infections, inflammation, and the aging process can all result in vision loss.

Eye-related causes of vision loss

Vision loss may be caused by conditions affecting the eye including:

• Age-related macular degeneration (disorder that causes loss of vision in the macula, the area of the retina responsible for seeing detail in the central vision)
• Cataracts (clouding or loss of transparency of the lens of the eye)
• Corneal edema (swelling and clouding of the normally transparent cornea)
• Eye infectionor inflammation (endophthalmitis, keratitis, or uveitis)
• Eye trauma
• Eye tumors
• Glaucoma (disorder that damages the optic nerve, often as a result of increased pressure in the eye)
• Macular edema(fluid accumulating within retinal layers)
• Presbyopia(hardening of the lens leading to decreased ability to focus the eye)
• Refractive errors such as myopia (nearsightedness), hyperopia (farsightedness), and astigmatism(irregularly shaped cornea)
• Retinal detachment(detachment of the light-sensing layer inside your eye from the blood vessels that provide it oxygen and nutrients)
• Retinitis pigmentosa (hereditary degeneration of the retina)
• Retinopathy of prematurity (abnormal development of blood vessels in the eye related to premature birth)
• Vitreous traction (macular hole)

Other causes of vision loss

Vision loss can also be caused by certain medications and by conditions that affect the brain or other parts of the body including:

• Diabetes(chronic disease that affects your body’s ability to use sugar for energy)
• Hypertension(high blood pressure)
• Inborn errors of metabolism
• Malnutrition
• Migraines
• Multiple sclerosis(disease that affects the brain and spinal cord causing weakness, coordination, balance difficulties, and other problems)
• Vasculitis(inflammation of blood vessels)
• Vitamin deficiency

Serious or life-threatening causes of vision loss

In some cases, vision loss may be a symptom of a serious or life-threatening condition that should be immediately evaluated in an emergency setting. These include:

• Brain tumor
• Head injury
• Increased intracranial pressure(high pressure inside the skull that is often due to brain swelling or hemorrhage)
• Ocular or orbital trauma
• Stroke
• Transient ischemic attack (temporary stroke-like symptoms that may be a warning sign of an impending stroke)

Questions for diagnosing the cause of vision loss

To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your vision loss including:

• When did you first notice your vision loss?
• Can you describe your vision loss?
• Is your vision loss constant, or does it come and go?
• Was your vision loss accompanied by any other symptoms?
• Did anything unusual, such as an injury or illness, precede the symptoms?
• Have you ever experienced vision loss before?
• Do you have any other symptoms?
• Do you have any other medical conditions?
• What medications are you taking?

What are the potential complications of vision loss?

Because vision loss can be due to serious diseases, failure to seek treatment can result in complications and permanent damage. Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:

• Adverse effects of treatment
• Brain damage
• Chronic ocular painor discomfort
• Disability
• Loss of vision and blindness
• Paralysis
• Progression of symptoms
• Spread of cancer
• Spread of infection 

https://en.wikipedia.org/wiki/Visual_impairmente